We analyzed data from 147 patients with suspected pertussis in San Luis Potosí, Mexico. Bordetella pertussis was detected by real-time polymerase chain reaction in 59 (40.1%) cases. The incidence of B. pertussis infection was 2.3 per 100,000 population. There were 6 deaths among the study patients. We conclude that the impact of pertussis in our state is significantly higher than previously estimated.